Hurricane Irma regained strength as it closed in on the Florida Keys early Sunday as forecasters monitored a crucial shift in its trajectory — just a few more miles to the west — that could keep its ferocious eye off the southwest Florida coast and over warm gulf water.

The hurricane re-strengthened to Category 4 status with maximum sustained winds near 130 mph (210 kph). The U.S. National Hurricane Center said Irma was expected to gain a little more strength as it moved through the Straits of Florida and remain a powerful hurricane as it approaches Florida.

Tens of thousands of people huddling in shelters watched for updates as the storm swung to the west, now potentially sparing Tampa as well Miami the catastrophic head-on blow forecasters had been warning about for days.

But those few miles meant St. Petersburg could get a direct hit, rather than its more populous twin across Tampa Bay. Neither city has suffered a major hurricane in nearly a century.

The leading edge of the immense storm bent palm trees and spit rain across South Florida, knocking out power to more than 170,000 homes and businesses, as the eye approached Key West.

"Tonight, I'm sweating. Tonight I'm scared to death," said 60-year-old Carol Walterson Stroud, who sought refuge in a senior center in Florida's southernmost city with her husband, granddaughter and dog. The streets emptied and shops were boarded up before the wind started to howl.

Florida Gov. Rick Scott had warned residents in the state's evacuation zones Saturday that "this is your last chance to make a good decision." About 6.4 million people were told to flee.

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But because the storm is 350 to 400 miles wide, the entire Florida peninsula was exposed. Forecasters said the greater Miami area of 6 million people could still get life-threatening hurricane winds and storm surge of 4 to 6 feet.

Irma was at one time the most powerful hurricane ever recorded in the open Atlantic with a peak wind speed of 185 mph (300 kph) last week. It left more than 20 people dead across the Caribbean and as it moved north over the Gulf of Mexico's bathtub-warm water of nearly 90 degrees, it was expected to regain strength.

Meteorologists predicted Irma would plow into the Tampa Bay area Monday morning. The area has not been struck by a major hurricane since 1921, when its population was about 10,000, National Hurricane Center spokesman Dennis Feltgen said. Now around 3 million people live there.

Jeff Weiner steps out of his trailer to smoke and look at the sky in the Sunshine Village mobile home community ahead of the arrival of Hurricane Irma, September 9, 2017 in Davie, Florida. CHIP SOMODEVILLA/AFP

Irma's course change caught many off guard and triggered a major round of last-minute evacuations in the Tampa area. Many businesses had yet to protect windows with plywood or hurricane shutters. Some locals grumbled about the forecast, even though Florida's west coast had long been included in the zone of probability.

"For five days, we were told it was going to be on the east coast, and then 24 hours before it hits, we're now told it's coming up the west coast," said Jeff Beerbohm, a 52-year-old entrepreneur in St. Petersburg. "As usual, the weatherman, I don't know why they're paid."

Nearly the entire Florida coastline remained under hurricane watches and warnings, and the latest projections could shift again, sparing or savaging other parts of the state.

Forecasters warned of storm surge as high as 15 feet (4.5 meters).

"This is going to sneak up on people," said Jamie Rhome, head of the hurricane center's storm surge unit.

The westward shift prompted Pinellas County, home to St. Petersburg, to order 260,000 people to leave, while Georgia scaled back evacuation orders for some coastal residents. Motorists heading inland from the Tampa area were allowed to drive on the shoulders.

At Germain Arena not far from Fort Myers, on Florida's southwestern corner, thousands waited in a snaking line for hours to gain a spot in the hockey venue-turned-shelter. "We'll never get in," Jamilla Bartley lamented in the parking lot.

The governor activated all 7,000 members of the Florida National Guard, and 30,000 guardsmen from elsewhere were on standby.

In the Orlando area, Walt Disney World, Universal Studios and Sea World all were closing Saturday. The Miami, Fort Lauderdale, Tampa and Orlando airports shut down.

Given its mammoth size and strength and its course up the peninsula, it could prove one of the most devastating hurricanes ever to hit Florida, and inflict damage on a scale not seen here in 25 years.

Haaretz.com, the online edition of Haaretz Newspaper in Israel, and analysis from Israel and the Middle East. Haaretz.com provides extensive and in-depth coverage of Israel, the Jewish World and the Middle East, including defense, diplomacy, the Arab-Israeli conflict, the peace process, Israeli politics, Jerusalem affairs, international relations, Iran, Iraq, Syria, Lebanon, the Palestinian Authority, the West Bank and the Gaza Strip, the Israeli business world and Jewish life in Israel and the Diaspora.